The Elements of Lean Manufacturing

Lean manufacturing is a set of related practices designed to reduce the time and cost of production while maintaining high quality standards. Henry Ford, with his introduction of the assembly line, is generally recognized as the father of lean manufacturing in America, but new strategies have been introduced over the years in the U.S. and Japan. All have the ultimate goal of minimizing waste and product defects and creating optimal efficiencies during every stage of production.

Kaizen, a Japanese term for “change” or “improvement,” serves as a sort of blueprint for lean production. It’s based on the philosophy that production improvements should be continual and line-worker involvement is critical because they have the best view of the situation. The ultimate goal is to reduce waste and improve process flow. Each step of current production is documented, with such factors as production time and distance traveled, scrap rate, changeovers, bottlenecks and product quality carefully measured. When process flow changes are made, new metrics are developed so that gains can be proven and quantified. At an automotive line, that might entail a closer physical proximity between wheel and axle assembly workstations to decrease production time.

The driving philosophy behind 5S workplace organization is that inefficient workplaces can’t yield efficient production. Plant management must take the following five steps to organize physical surroundings before real change can be made: sort, set in order, shine, standardize and sustain. Sorting involves designing stations for smooth and efficient work flow. Each tool is scrutinized for its value to the job, and irrelevant items are removed. The concept of setting in order involves organizing critical tools and equipment for proper storage and easy accessibility. Shining refers to plant cleanliness. In addition to creating a more appealing work environment, this makes it easier to see machine leaks and other failures. Standardizing is a way of formalizing practices and assigning responsibilities that will maintain the effect of the first three “S” strategies. Sustaining is the ability to maintain and continually enhance these efficiency practices. What are the minimum number of steps and processes needed in the car plant example? Anything more would be discontinued for inefficiency.

Cellular manufacturing, also known as “continuous product flow,” recognizes that for maximum efficiency, each stage of production must work in smooth unison with adjoining stages. With that in mind, manufacturers configure their plant so that production can flow quickly and easily from one workstation, or “cell,” to the next. Machinery and equipment are regularly maintained to avoid downtime, and the plant is designed for the efficient staging of inventory. Raw materials in the car plant example are positioned where needed for the most strategic work flow.

The strategy of just-in-time production was developed by the Japanese automaker Toyota in the 1970s as a way of shaving inventory costs. In addition to the actual cost of buying and holding raw materials that can’t immediately be used and sold, manufacturers must also assume the labor costs of handling and storing inventory and the physical cost of warehousing that material. The philosophy behind just-in-time production is to buy and store only the bare minimum amount of materials needed for each stage of production. This requires a close relationship between cells so that the work flows from stage to stage without bottlenecks from a shortage of materials. In other words, carburetors are expensive and unwieldy to warehouse, so the auto plant example will take daily delivery and turn over inventory in 24 hours.